A conventional semiconductor wafer fabrication process entails detection and inspection of defects in the patterned surface of a specimen wafer. The in-process inspection for defects is typically accomplished with the use of an operator-controlled inspection station that includes a microscope and a television-type display monitor for viewing the minute detail of the patterned surface in a small region of the wafer.
The wafer is typically secured by vacuum pressure or other means to an X-Y translation stage that moves the wafer in a horizontal plane. The microscope optically communicates with a fixed region in space above the X-Y stage, the fixed region being defined by the field of view of the microscope objective. The X-Y stage moves the wafer to selectable positions in the horizontal plane to present different regions of the wafer within the field of view of the microscope objective. A video camera optically coupled to the microscope provides video signals representative of the region of the wafer presented to the microscope objective. The operator is, therefore, able to select a region of the wafer for inspection and view the region through the microscope eyepiece or a video image of the region displayed on the monitor.
There are several design considerations affecting the physical layout of and equipment used in a specimen inspection station. Such design considerations stem primarily from the presence of an operator and her or his movements during normal use of the inspection station.
First, the operator uses a keyboard to manually enter data delivered to a computer that generates commands to operate the X-Y stage and perform other functions necessary to locate, identify, and classify defects in the specimen wafer under inspection. Vibration isolation is, therefore, sometimes used to prevent normal operator movements from affecting the stability of the wafer region positioned within the field of view of the microscope objective.
Second, human contamination introduced by the operator is a significant contributor to in-process wafer defects. To combat this problem, special equipment providing a clean room environment is sometimes used.
Third, the ergonomics of coordinating the placement of operator equipment such as the keyboard, the microscope, and display monitor for operator convenience and ease of use dictates the layout and size of a work space needed for the specimen inspection station components. The size of the specimen that is to undergo inspection can also affect the size of the work space.
Finally, the horizontal disposition of a very large area specimen on the X-Y stage can cause the specimen to deflect under its own weight and thereby necessitate the use of a stage having a large surface area to reduce the amount of stress borne by the specimen during inspection.